Electrically driven, self-contained in-tank gear rotor fuel pumps have been used for delivering fuel from a supply tank to an internal combustion engine of a motor vehicle. This type of pump produces a steady, non-surging, highly pressurized flow of fuel making it ideal for use with modern fuel injection systems. The design is also highly tolerant of fuel supply line pressure transients commonly associated with the abrupt opening and closing of individual fuel injectors.
Typically, these pumps consist of a housing having an electric motor with an armature journalled for rotation between a pair of end caps and coupled to a gear rotor pump assembly. The armature is carried by a shaft received at one end in a bearing in one end cap and at its other end in a bearing in the other end cap. Such a pump is disclosed in U.S. Pat. No. 5,122,039 which is assigned to the assignee hereof.
A problem with these pumps is that they can be noisy during operation which can be objectionable to vehicle occupants. For example, undesirable pump noise can be created by the mechanical interaction of moving parts within the housing during pump operation. Even worse, should the bearings be misaligned when the end caps are assembled to the housing, the armature can become dynamically unbalanced about its axis of rotation and the gear rotor assembly can be slightly radially and/or axially mislocated within the housing dramatically increasing pump noise.
Not only can bearing misalignment contribute to pump noise, it can also adversely affect performance. For example, should the armature be misaligned relative to the stator of the electric motor causing the spacing between the armature and stator to undesirably vary, motor performance can be detrimentally affected. Similarly, if misalignment affects the spacing between the gear rotor pump assembly and the interior surface of the inlet end cap, the maximum volumetric flow rate of the pump assembly can also be reduced. In combination, both of these problems caused by bearing misalignment can seriously degrade pump performance. Unfortunately, the difficulty of repeatedly manufacturing a large number of pumps of this construction having a motor assembly which is consistently properly aligned makes these misalignment problems common.
Another problem with these fuel pumps is noise contributed due to pressure pulses created by fuel being expelled from the pump assembly under high pressure and turbulence in the flow of fuel entering the pump inlet. Although the pressure pulse damper of the gear rotor-type fuel pump disclosed in the aforementioned patent has enjoyed substantial commercial acceptance and success in reducing fuel pump noise, particularly by dampening fuel pressure pulses, improvements nonetheless remain desirable. A pump utilizing such a damper requires a cavity within the pump downstream of the gear rotor pump assembly, increasing the length and number of parts of the pump. Also, the reliability and useful life of these flexible plastic dampers is highly dependent upon its design geometry and cyclical loading which requires careful design and control of part geometry and quality to obtain a reliable damper having an extended service life.